Chemical-mechanical planarization (CMP) systems use a polishing head to press and rotate a substrate against a polishing pad during processing. During the polishing process, a substrate within a polishing head is held within the head using a retaining ring which encircles the substrate and prevents the substrate from being dragged out of the polishing head by the relative movement of the polishing pad. The inventors of the present invention have noticed that in some cases, the retaining ring may prematurely wear. Thus, what is needed are improved methods and apparatus for retaining a substrate within a polishing head during processing.